[Andy]

I hesitate to offer anything. I have been trying to salvage the lock and lever from two drops for a month or more. I soaked them in Evap o rust for weeks. The Evapo rust got the locks nice and free but did absolutly nothing as to breaking the bond holding the locks in. I finally cut the drops apart to get the parts out. Even with a cut that split the hole for the lock and a relief cut on the other side, it was still stuck. I really don't know what would free them up. I have been using vinegar on some parts with great sucess. The only thing the vinegar could hurt would be the springs in the lock, I have seen NO evidence of the vinegar eating anything but rust so that would be my choice.
It may take months to get it loose.
Heat would help but it would be dangerous to the lock. The brass expands more than the iron and might swedge the case of the lock.
Maybe a bump to the top will get a responce from someone with knowledge.